1. Field of the Invention
The invention relates generally to a system and method for dynamically optimizing parameters of a text-to-speech (“TTS”) system in response to automotive vehicle environmental conditions in order to maximize the intelligibility of a synthesized TTS voice. In particular, the invention is focused on a method of optimizing the TTS voice while minimizing distractions to a vehicle operator.
2. Description of Related Art
Systems incorporating text-to-speech (“TTS”) engines or synthesizers coupled to a database of textual data are well known and continue to find an ever-increasing number of applications. For example, automobiles equipped with TTS and speech-recognition capabilities simplify tasks that would otherwise distract a driver from driving. The uses of TTS systems in vehicles include controlling electronic systems aboard the vehicle, such as navigation systems or audio systems, receiving critical emergency broadcasts, and placing telephone calls, among others.
Certain environmental conditions, such as vehicle speed, interior noise, lighting conditions, and weather conditions, among others, can affect a driver's concentration level and may affect the driver's ability to pay attention to and comprehend TTS voice prompts. Some existing systems attempt to compensate for certain environmental conditions while generating TTS voice prompts for automotive vehicles. For example, some systems monitor vehicle speed or other vehicle operating parameters and attempt to schedule messages for time periods when a driver will be better equipped to listen to them, such as when a driver is stopped or moving slowly. Other systems relating to vehicle navigation may use vehicle speed and estimated driver reaction times to give verbal instructions, such as “turn right,” at appropriate times.
A co-pending application by the same inventors entitled, “VARIABLE TEXT-TO-SPEECH FOR AUTOMOTIVE APPLICATION,” and incorporated herein by reference, describes a system addressing the problem that in responding to changing environmental conditions, a driver may be required to put more concentration into driving and controlling a vehicle, leaving less mental power available for other activities, including listening to and concentrating on a TTS system. In fact, under stressful driving conditions, a driver may perceive a slower TTS voice as being normal and a normal-speed voice as being too fast. On the other hand, under non-stressful conditions, a driver may require less mental effort, and a slower TTS voice may irritate or bore the driver. Likewise, other parameters of a TTS voice, such as pitch or volume, may also require tuning to optimize intelligibility to a driver under different environmental conditions. The above-referenced co-pending application provides a system that analyzes vehicle sensor data in order to apply corrections to various parameters of the TTS synthesized voice, such as voice speed, pitch, and volume, among others, to compensate for environmental conditions to achieve improved intelligibility across a wide variety of vehicle operating conditions.
However, when environmental or operating conditions change abruptly, applying calculated changes to a TTS system immediately can cause discontinuous changes in the character of a TTS voice that can be distracting to an operator of a vehicle. For example, while a slower speed of a TTS voice may not be noticeable to a driver under stressful driving conditions, an abrupt change from a normal to a slower-speed voice, as a driver accelerates, for example, may be noticeable and distracting. Thus, it would be useful to provide a system that applies changes to the character of a TTS voice in a manner that efficiently achieves near-optimal performance of the character of a TTS voice while making changes in a way that is unnoticeable and non-distracting to a vehicle operator.